scholarly journals A Review of Secondary Flow in Inertial Microfluidics

Micromachines ◽  
2020 ◽  
Vol 11 (5) ◽  
pp. 461 ◽  
Author(s):  
Qianbin Zhao ◽  
Dan Yuan ◽  
Jun Zhang ◽  
Weihua Li
Keyword(s):  
Secondary Flow ◽  
Flow Speed ◽  
Particle Migration ◽  
Channel Structure ◽  
Multiple Equilibrium ◽  
Hydrodynamic Drag ◽  
Hydrodynamic Effect ◽  
Inertial Microfluidics ◽  
Microfluidic Technology ◽  
Wide Range

Inertial microfluidic technology, which can manipulate the target particle entirely relying on the microchannel characteristic geometry and intrinsic hydrodynamic effect, has attracted great attention due to its fascinating advantages of high throughput, simplicity, high resolution and low cost. As a passive microfluidic technology, inertial microfluidics can precisely focus, separate, mix or trap target particles in a continuous and high-flow-speed manner without any extra external force field. Therefore, it is promising and has great potential for a wide range of industrial, biomedical and clinical applications. In the regime of inertial microfluidics, particle migration due to inertial effects forms multiple equilibrium positions in straight channels. However, this is not promising for particle detection and separation. Secondary flow, which is a relatively minor flow perpendicular to the primary flow, may reduce the number of equilibrium positions as well as modify the location of particles focusing within channel cross sections by applying an additional hydrodynamic drag. For secondary flow, the pattern and magnitude can be controlled by the well-designed channel structure, such as curvature or disturbance obstacle. The magnitude and form of generated secondary flow are greatly dependent on the disturbing microstructure. Therefore, many inventive and delicate applications of secondary flow in inertial microfluidics have been reported. In this review, we comprehensively summarize the usage of the secondary flow in inertial microfluidics.

Small Molecule Permeation Across Membrane Channels: Chemical Modification to Quantify Transport Across OmpF

2018 ◽  
Author(s):  
Jiajun Wang ◽  
Jayesh Arun Bafna ◽  
Satya Prathyusha Bhamidimarri ◽  
Mathias Winterhalter
Keyword(s):  
Dwell Time ◽  
Covalent Binding ◽  
Channel Structure ◽  
Ion Current ◽  
E Coli ◽  
Current Fluctuation ◽  
Wide Range ◽  
Outer Membrane Channel ◽  
Biological Channels ◽  
Constriction Region

Biological channels facilitate the exchange of small molecules across membranes, but surprisingly there is a lack of general tools for the identification and quantification of transport (i.e., translocation and binding). Analyzing the ion current fluctuation of a typical channel with its constriction region in the middle does not allow a direct conclusion on successful transport. For this, we created an additional barrier acting as a molecular counter at the exit of the channel. To identify permeation, we mainly read the molecule residence time in the channel lumen as the indicator whether the molecule reached the exit of the channel. As an example, here we use the well-studied porin, OmpF, an outer membrane channel from <i>E. coli</i>. Inspection of the channel structure suggests that aspartic acid at position 181 is located below the constriction region (CR) and we subsequently mutated this residue to cysteine, where else cysteine free and functionalized it by covalent binding with 2-sulfonatoethyl methanethiosulfonate (MTSES) or the larger glutathione (GLT) blockers. Using the dwell time as the signal for transport, we found that both mono-arginine and tri-arginine permeation process is prolonged by 20% and 50% respectively through OmpF<sub>E181C</sub>MTSES, while the larger sized blocker modification OmpF<sub>E181C</sub>GLT drastically decreased the permeation of mono-arginine by 9-fold and even blocked the pathway of the tri-arginine. In case of the hepta-arginine as substrate, both chemical modifications led to an identical ‘blocked’ pattern observed by the dwell time of ion current fluctuation of the OmpF<sub>wt</sub>. As an instance for antibiotic permeation, we analyzed norfloxacin, a fluoroquinolone antimicrobial agent. The modulation of the interaction dwell time suggests possible successful permeation of norfloxacin across OmpF<sub>wt</sub>. This approach may discriminate blockages from translocation events for a wide range of substrates. A potential application could be screening for scaffolds to improve the permeability of antibiotics.

scholarly journals Computational Ion Channel Research: from the Application of Artificial Intelligence to Molecular Dynamics Simulations.

2020 ◽  
Vol 55 (S3) ◽  
pp. 14-45
Keyword(s):  
Artificial Intelligence ◽  
Molecular Dynamics ◽  
Ion Channels ◽  
Ion Channel ◽  
Computational Methods ◽  
Homology Modelling ◽  
Channel Structure ◽  
Learning Approaches ◽  
Qsar Analysis ◽  
Wide Range

Although ion channels are crucial in many physiological processes and constitute an important class of drug targets, much is still unclear about their function and possible malfunctions that lead to diseases. In recent years, computational methods have evolved into important and invaluable approaches for studying ion channels and their functions. This is mainly due to their demanding mechanism of action where a static picture of an ion channel structure is often insufficient to fully understand the underlying mechanism. Therefore, the use of computational methods is as important as chemical-biological based experimental methods for a better understanding of ion channels. This review provides an overview on a variety of computational methods and software specific to the field of ion-channels. Artificial intelligence (or more precisely machine learning) approaches are applied for the sequence-based prediction of ion channel family, or topology of the transmembrane region. In case sufficient data on ion channel modulators is available, these methods can also be applied for quantitative structureactivity relationship (QSAR) analysis. Molecular dynamics (MD) simulations combined with computational molecular design methods such as docking can be used for analysing the function of ion channels including ion conductance, different conformational states, binding sites and ligand interactions, and the influence of mutations on their function. In the absence of a three-dimensional protein structure, homology modelling can be applied to create a model of your ion channel structure of interest. Besides highlighting a wide range of successful applications, we will also provide a basic introduction to the most important computational methods and discuss best practices to get a rough idea of possible applications and risks.

Extended Stokes series: laminar flow through a loosely coiled pipe

1978 ◽  
Vol 86 (1) ◽  
pp. 129-145 ◽  
Author(s):  
Milton Van Dyke
Keyword(s):  
Laminar Flow ◽  
Flow Speed ◽  
Square Root ◽  
Mean Flow ◽  
Dean Number ◽  
Curvature Ratio ◽  
Wide Range ◽  
Square Root Singularity ◽  
Flow Through ◽  
The One

Dean's series for steady fully developed laminar flow through a toroidal pipe of small curvature ratio has been extended by computer to 24 terms. Analysis suggests that convergence is limited by a square-root singularity on the negative axis of the square of the Dean number. An Euler transformation and extraction of the leading and secondary singularities at infinity render the series accurate for all Dean numbers. For curvature ratios no greater than$\frac{1}{250} $, experimental measurements of the laminar friction factor agree with the theory over a wide range of Dean numbers. In particular, they confirm our conclusion that the friction in a loosely coiled pipe grows asymptotically as the one-quarter power of the Dean number based on mean flow speed. This contradicts a number of incomplete boundary-layer analyses in the literature, which predict a square-root variation.

Development of Surface Skin Friction Measurement Technique Based on Compliant Coatings

2007 ◽  
Author(s):  
Nobuyoshi Fujimatsu ◽  
Isao Misu
Keyword(s):  
Skin Friction ◽  
Friction Force ◽  
Force Measurement ◽  
A Priori ◽  
Ccd Camera ◽  
Flow Speed ◽  
Polymeric Film ◽  
Wide Range ◽  
Unsteady Characteristics

New method and means are proposed to measure the skin friction force on an aerodynamic surface based on elastic deformations of silicon rubber and gel coatings. One of characteristics is soft and easy to deform. Object is coated by elastic polymeric film with known shear modulus. Two images between wind-on and wind-off are taken using the CCD camera. The displacement of coating is calculated from the correlation of two images. There are two ways to calibrate the skin friction force to the displacement of coatings. These methods are tested and compared to quantitative skin friction force measurement. One is based on measuring the characteristics of the polymeric film using visco-elastic measurement system. This way is called as a priori calibration. The other way is accomplished from the relation between the skin friction force measured by the PHF embedded on the object and the displacement around there and is known as In-situ method. Characteristics of the coatings such as the displacement and the time response can be easily controlled by the compounding ratio of hardener. We conduct the theoretical analysis for the elastic polymer film and propose the material properties of the coatings required to measure the surface skin friction in the wide range of flow speed. The skin friction over the plate is measured using this technique in various Reynolds number. The traditional measurement using the hot wire anemometry is conducted to validate this technique. The time averaged measurements of this technique are in good agreement with the traditional results. However, the unsteady characteristics of surface skin friction are not captured by the lack of time resolution of the CCD camera.

A Geometry Generation Framework for Contoured Endwalls

2019 ◽  
Author(s):  
L. E. Wood ◽  
R. R. Jones ◽  
O. J. Pountney ◽  
J. A. Scobie ◽  
D. A. S. Rees ◽  
...  
Keyword(s):  
Secondary Flow ◽  
Three Dimensional ◽  
Aerodynamic Loss ◽  
Construction Methods ◽  
Novel Approach ◽  
Wide Range ◽  
Blade Row ◽  
Flow Features ◽  
Flow Effects ◽  
Geometric Variation

Abstract The mainstream, or primary, flow in a gas turbine annulus is characteristically two-dimensional over the mid-span region of the blading, where the radial flow is almost negligible. Contrastingly, the flow in the endwall and tip regions of the blading is highly three-dimensional, characterised by boundary layer effects, secondary flow features and interaction with cooling flows. Engine designers employ geometric contouring of the endwall region in order to reduce secondary flow effects and subsequently minimise their contribution to aerodynamic loss. Such is the geometric variation of vane and blade profiles — which has become a proprietary art form — the specification of an effective endwall geometry is equally unique to each blade-row. Endwall design methods, which are often directly coupled to aerodynamic optimisers, are widely developed to assist with the generation of contoured surfaces. Most of these construction methods are limited to the blade-row under investigation, while few demonstrate the controllability required to offer a universal platform for endwall design. This paper presents a Geometry Generation Framework (GGF) for the generation of contoured endwalls. The framework employs an adaptable meshing strategy, capable of being applied to any vane or blade, and a versatile function-based approach to defining the endwall shape. The flexibility of this novel approach is demonstrated by recreating a selection of endwalls from the literature, which were selected for their wide-range of contouring approaches.

On the causal behaviour of flow over an elastic wall

1999 ◽  
Vol 396 ◽  
pp. 319-344 ◽  
Author(s):  
R. J. LINGWOOD ◽  
N. PEAKE
Keyword(s):  
Shear Layer ◽  
Finite Time ◽  
Radiation Condition ◽  
Flow Speed ◽  
Uniform Flow ◽  
Dispersion Function ◽  
Mean Flow ◽  
Wide Range ◽  
Line Force ◽  
Layer Flow

In this paper we consider the causal response of the inviscid shear-layer flow over an elastic surface to excitation by a time-harmonic line force. In the case of uniform flow, Brazier-Smith & Scott (1984) and Crighton & Oswell (1991) have analysed the long-time limit of the response. They find that the system is absolutely unstable for sufficiently high flow speeds, and that at lower speeds there exist certain anomalous neutral modes with group velocity directed towards the driver (in contradiction of the usual radiation condition of out-going disturbances). Our aim in this paper is to repeat their analysis for more realistic shear profiles, and in particular to determine whether or not the uniform-flow results can be regained in the limit in which the shear-layer thickness on a length scale based on the fluid loading, denoted ε, becomes small. For a simple broken-line linear shear profile we find that the results are qualitatively similar to those for uniform flow. However, for the more realistic Blasius profile very significant differences arise, essentially due to the presence of the critical layer. In particular, we find that as ε → 0 the minimum flow speed required for absolute instability is pushed to considerably higher values than was found for uniform flow, leading us to conclude that the uniform-flow problem is an unattainable singular limit of our more general problem. In contrast, we find that the uniform-flow anomalous modes (written as exp (ikx − iωt), say) do persist for non-zero shear over a wide range of ε, although now becoming non-neutral. Unlike the case of uniform flow, however, the k-loci of these modes can now change direction more than once as the imaginary part of ω is increased, and we describe the connection between this behaviour and local properties of the dispersion function. Finally, in order to investigate whether or not these anomalous modes might be realizable at a finite time after the driver is switched on, we evaluate the double Fourier inversion integrals for the unsteady flow numerically. We find that the anomalous mode is indeed present at finite time, once initial transients have propagated away, not only for impulsive start-up but also when the forcing amplitude is allowed to grow slowly from a small value at some initial instant. This behaviour has significant implications for the application of standard radiation conditions in wave problems with mean flow.

Effect of Circumferentially Nonuniform Heating on Laminar Combined Convection in a Horizontal Tube

1978 ◽  
Vol 100 (1) ◽  
pp. 63-70 ◽  
Author(s):  
S. V. Patankar ◽  
S. Ramadhyani ◽  
E. M. Sparrow
Keyword(s):  
Heat Transfer ◽  
Secondary Flow ◽  
Forced Convection ◽  
Horizontal Tube ◽  
Nonuniform Heating ◽  
Convection Flow ◽  
Nusselt Numbers ◽  
Wide Range ◽  
Bottom Heating ◽  
Over The Top

An analytical study has been made of how the circumferential distribution of the wall heat flux affects the forced/natural convection flow and heat transfer in a horizontal tube. Two heating conditions were investigated, one in which the tube was uniformly heated over the top half and insulated over the bottom, and the other in which the heated and insulated portions were reversed. The results were obtained numerically for a wide range of the governing buoyancy parameter and for Prandtl numbers of 0.7 and 5. It was found that bottom heating gives rise to a vigorous buoyancy-induced secondary flow, with the result that the average Nusselt numbers are much higher than those for pure forced convection, while the local Nusselt numbers are nearly circumferentially uniform. A less vigorous secondary flow is induced in the case of top heating because of temperature stratification, with average Nusselt numbers that are substantially lower than those for bottom heating and with large circumferential variations of the local Nusselt number. The friction factor is also increased by the secondary flow, but much less than the average heat transfer coefficient. It was also demonstrated that the buoyancy effects are governed solely by a modified Grashof number, without regard for the Reynolds number of the forced convection flow.

Recent Research on Cascade-Flow Problems

1966 ◽  
Vol 88 (1) ◽  
pp. 221-228 ◽  
Author(s):  
H. Schlichting ◽  
A. Das
Keyword(s):  
Reynolds Number ◽  
Secondary Flow ◽  
High Speed ◽  
Research Work ◽  
Reynolds Numbers ◽  
Tip Clearance ◽  
Flow Problems ◽  
Flow Losses ◽  
Cascade Flow ◽  
Wide Range

A survey is given of extensive research work on cascade-flow problems carried out in recent years in Germany. A considerable part of this work was done in the Variable Density High Speed Cascade Wind Tunnel of the Deutsche Forschungsanstalt fu¨r Luftfahrt at Braunschweig, in which the Reynolds number and the Mach number of the cascade can be varied independently. For compressor cascades with blades of different thickness ratio extensive measurements of the aerodynamic coefficients have been carried out in a wide range of Mach numbers and Reynolds numbers. For very low Reynolds numbers, as they occur for jet engines in high-altitude flight, the influence of turbulence level on loss coefficients has been investigated. Furthermore, comprehensive investigations on secondary-flow losses are reported. The most important parameters in this connection are the ratio of blade length to blade chord, the tip clearance, the Reynolds number, and the deflection of the flow in the cascade. The influence of all these parameters on the secondary-flow losses has been clarified to a certain extent.

Virtual Height Aided Solar Chimney: A New Design

2011 ◽  
Author(s):  
Khaled I. E. Ahmed ◽  
Ali K. Abdel-Rahman ◽  
Mahmoud Ahmed ◽  
Wael M. Khairaldien
Keyword(s):  
Electric Power ◽  
Co2 Emissions ◽  
Conversion Efficiency ◽  
Numerical Study ◽  
Air Flow ◽  
Flow Speed ◽  
Numerical Results ◽  
Solar Chimney ◽  
Virtual Height ◽  
Wide Range

Renewable energy source deployment is growing rapidly as it reduces CO2 emissions and increases diversity and security of supply. Solar chimney (SC) is a promising large-scale power technology, which absorbs solar radiation and converts parts of solar energy into electric power free of CO2 emissions. A major problem of Solar Chimney Power Plant (SCPP) is its low conversion efficiency as determined by the thermal performance of the system. However, the conversion efficiency of SCPP significantly increases with the SC height increase. The current paper proposes a new design of a virtual height aided solar chimney. In this new system the solar chimney is aided with a passive cooling system at the top of the chimney and a passive solar heater at its base to virtually mimic larger heights of the chimney. The new design has been simulated numerically for development and optimization. The numerical study is done in two stages to examine this concept. In the first stage, numerical results are obtained for the effect of the chimney height on the inside air flow speed. Then, in the second stage, the effect of decreasing the temperature at the chimney exit and the effect of increasing the temperature at the chimney base on the air flow speed are examined separately for small chimney heights. Then the combined effect of the two actions is investigated at a wide range of chimney heights. The numerical results have shown that the localized base heating and exit cooling have significantly enhanced the chimney performance for chimney heights up to 500m. A chimney with height of 300m gains an increase in the air velocity more than 25% due to the heating and cooling actions. Virtual height aided Chimney with original height of 300m acts similarly to a conventional chimney with height of 500m due to the effect of base heating and exit cooling actions. This air flow velocity increase reflects 100% increase in the expected generated electric power. Further detailed results are presented and discussed.

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